A subject matter of the present invention is a novel process for the preparation of tetrakis(pentafluorophenyl)borate derivatives.
The borate derivatives obtained according to the invention are products of use as intermediates in the preparation of catalysts for crosslinking and/or for polymerizing by the thermal route, by the photochemical route and/or under an electron beam.
These intermediates can also be used to prepare catalysts of Ziegler-Natta type for the polymerization of olefins, such as those disclosed, for example, in the documents WO 9412547 and EP-A-277 004.
In recent years, numerous documents have been published relating to the use of the polymerization catalysts obtained from tetrakis(pentafluorophenyl)borate derivatives. Mention will in particular be made, by way of examples, of the Patents EP 562 897 and EP 56 922 from Rhodia Chimie.
Other documents relate to the preparation of tetrakis(pentafluorophenyl)borate derivatives. For example, the document EP 604 961 discloses access to the borates MB(C6F5)4 by the magnesium derivative route and the document EP 608 563 discloses access to the product LiB(C6F5)4 from pentafluorobenzene in solution in ethyl ether.
However, the processes, in particular industrial processes, disclosed in the literature are not satisfactory. In particular, the use of an organomagnesium derivative does not allow a high yield to be obtained from the reaction for the conversion of BR3, more specifically BCl3, to B(C6F5)4xe2x88x92. Likewise, the use of solvents, such as ethyl ether or isopropyl ether, does not allow the industrial processes to be optimized in terms of reaction time and of yield of final product. By way of example, the use of boron trichloride in the gaseous form cannot be envisaged with ethyl ether or isopropyl ether. This is because the BCl3 forms, with these ethers, relatively stable complexes which do not react to any extent with the compound LiC6F5.
A subject matter of the present invention is a novel optimized process for the preparation of tetrakis(pentafluorophenyl)borate derivatives which makes it possible to landings the abovementioned disadvantages.
Among the numerous advantages of this novel process, the purity of the tetrakis(pentafluorobenzene)borate derivatives and in particular of potassium tetrakis(pentafluorobenzene)borate is improved. In addition, the novel process generates only a very small amount of B(C6F5)3 byproduct.
Thus, a novel process for the preparation of tetrakis(pentafluorophenyl)borate of general formula MB(C6F5)4 (I), M being chosen from Na+, Li+ or K+, has thus now been developed, in which process:
(a) a solution of C6F5X, X being chosen from H, Cl, Br and I, in anhydrous butyl ether is brought into contact with an alkyllithium, the C6F5X/alkyllithium molar ratio being between 1 and 1.1 and the alkyl radical being chosen from linear or branched radicals comprising from 1 to 10 carbon atoms and preferably a hexyl radical;
(b) the resulting product is brought into contact with BR3 (II), undissolved beforehand before its use, R, which is identical or different, being chosen from a chlorine atom, a fluorine atom, a bromine atom and an alkoxy radical comprising from 1 to 4 carbon atoms.
BR3 used thus makes it possible to dispense with a conditioning stage before its introduction. This direct use of BR3 greatly improves the reaction rate within the mixture (direct contacting).
Furthermore, the choice of anhydrous butyl ether as solvent and of BR3 makes it possible to avoid the formation of complexes which may be stable and harmful to the reactivity of the products employed in the preparation process.
According to a first specific form of the invention, BR3 is advantageously introduced into the reaction mixture in the gaseous form.
According to a second specific form of the invention, BR3 is boron trichloride.
Mention will be made, as examples of other BR3 (II) products, of BF3.OEt2, B(OMe)3, BBr3, and the like.
As an example of an industrial preparation process according to the invention, the stages below are followed for the preparation of potassium tetrakis(pentafluorophenyl)borate:
(a) the anhydrous butyl ether and the pentafluorobenzene are introduced into the reactor and are then mixed with stirring while cooling to a temperature of approximately xe2x88x9270xc2x0 C.,
(b) a solution of alkyllithium and preferably of hexyllithium is run into the reaction mixture at a controlled rate,
(c) undissolved BR3, preferably boron trichloride, is then added to the reaction mixture and the mixture is allowed to rise to a temperature in the region of 0xc2x0 C.,
(d) an aqueous potassium chloride solution is then introduced, the mixture subsequently being stirred at ambient temperature,
(e) after separating by settling, the aqueous phase is withdrawn and a potassium chloride solution is added before distilling under a reduced pressure, preferably of less than 500 mbar,
(f) after filtering and optionally washing, the tetrakis(pentafluorophenyl)borate derivative of general formula KB(C6F5)4 is recovered.